Composites are widely used in restorative dentistry, but significant deficiencies in the composite longevity still exist. The majority of dental composie restorations are estimated to fail within the first 10 years of service, mainly due to the formatio of bacterial biofilm-induced caries at the tooth-material interface. Therefore, to develop longer lasting dental restorative materials, it is essential to understand the fundamental chemistry and biology at the interface of the composites and the oral biofilm. Currently, the analytical techniques to study this interface at a sufficiently high spatial resolution to measure bacterial metabolic activity do not exist. Hence, the overall objective of this proposed study is to determine the effects of metal ion (i.e. calcium) release from dental composites on the biofilm growth, metabolism and gene expression. Bioactive glass-containing dental composites that release calcium ions as well as neutralize pH will be used as a model biofilm growth substrate. The central hypotheses are to test whether varying amounts of calcium ions have any significant effect on the biofilm growth and determine whether the metal ions have any differential growth effects on lactate-producing Streptococcus mutans (Sm) and lactate-consuming Veillonella parvula (Vp), such that the overall local pH is equal or greater than 5.5 to prevent demineralization of adjacent tooth structures. We will approach our hypothesis with the following specific aims: We will fabricate ultramicro-sensors for pH, calcium ions and lactate (Specific aim 1). Then, these microsensors will be assessed for use as a scanning electrochemical microscopy (SECM) probe to quantitatively map the chemical microenvironment above dental composites containing bioactive glass, with and without growing bacteria biofilm (s) (Sm and Vp). This innovative technique will help to quantify the local lactate concentration and the resultant overall local pH in the presence of Sm and Vp while exposed to varying amounts of calcium ions released from the composites. This information will ultimately lead to the design of new dental materials with optimal ion releasing property such that the overall local pH remains at 5.5 or higher (Specific aim 2). Finally, SECM mapping data will be used to determine the interdependence of different composites formulations, the real-time redox environment and polymicrobial biofilm gene expression (Specific aim 3). The proposed research is a significant step towards predicting the next-generation smart dental composites, which will be able to deter the growth of acidogenic biofilms and to maintain a balance in the local pH and ultimately increase the lifespan of dental composite restorations.